Hot-gas machine comprising a heat transfer device

ABSTRACT

A hot-gas machine in which a gaseous medium performs a closed thermodynamic cycle, includes a heat conveying device which is capable of conveying heat by means of an evaporation condensation process from a heat source to the heater of the machine. This device comprises at least two closed spaces containing conveying-medium and arranged one after the other in the direction of heat conveyance, the distal ends of these spaces being provided with heat transferring walls across which heat can be conducted from the heat source to the conveying medium, or the conveying medium can give off heat to the heater; the proximal ends of these spaces comprises further heat-transferring walls, between which a switching element is provided for the establishment of a thermal and variable contact between these further walls.

United States Patent Dirne et al.

[ HOT-GAS MACHINE CONIPRISING A HEAT TRANSFER DEVICE [72] Inventors:Adrianus Petr-us Dime; George A]- bert Apolonia Asselmam Herman HenricusMaria van der Aa, all of Emmasingel, Eindhoven, Netherlands [73]Assignee: U.S. Philips Corporation, .New

York, NY.

[22] Filed: Nov. 27, 1970 21 Appl. No.: 93,104

30 Foreign Application Priority Data 1451 Nov. 14, 1972 2,820,134 1/1958Kobayashi ..l65/l0$ FOREIGN PATENTS OR APPLICATIONS 1,122,970 1962Germany 165/96 63 ,822 1949 Netherlands ..60/ 24 Primary Examiner-Martin P. Schwadron Assistant Examiner-'A. M. Ostrager Attorney-FrankR. Trifari ABSTRACT A hot-gas machine in which a gaseous medium performsa closed thermodynamic cycle, includes a heat conveying device which is.capable of conveying heat by means of an evaporation condensationprocess from a heat source to the heater of the machine. This devicecomprises at least two closed spaces containing conveying-medium andarranged one after the other in the direction of heat conveyance, thedistal ends of these spaces being provided with heat transferring wallsacross which heat can be conducted from the heat source to the conveyingmedium, or the conveying medium can give off heat to the heater; theproximal ends of these spaces comprises further heat-transferring walls,between which a switching element is provided for the establishment of athermal and variable contact between these further walls.

14 Clains, 7 Drawing Figures P'ATE'NTEDKUV 14 m2 SHEEII or 3 Fig.2

INVEX'IORS RIANUS P. DIRNE AD GEORGE A.A. ASSELMAN BYHERMAN H.M. VAN DERAA AGE 7' SHEET 2 0F 3 -a' I a l lg; L2 28 LH. #111 Fig.3

I NVE X TORS ADRIANUS P. DIRNE GEORGE A.A. ASSELMAN HERMAN H M. VAN DERAA AG-EN P'A'TENTEI'Jnuv 14 m2 SHEET 3 OF 3 2. mp RE. I

INVIJN'IORS AD RIANUS R DI RNE GEORGE A.A. ASSELMAN HERMAN H.M. VAN DERAA HOT-GAS MACHINE COMPRISING A HEAT TRANSFER DEVICE BACKGROUND OF THEINVENTION The invention relates to a hot-gas machine, for example, ahot-gas reciprocating engine or a hot-gas turbine, in which a gaseousmedium performs a closed thermodynamic cycle. The machine includes aheater in which the cyclic medium receives heat from the outside from asource of heat; particularly a heat accumulator, a heat transfer deviceis provided between the heat source and the heater, said devicecontaining a heat transporting medium which absorbs heat from the heatsource while changing over from the liquid phase to the vapor phase, andgiving off heat to the heater while changing-over from the vapor phaseinto the liquid phase. A prior art machine of this kind is known fromDutch Pat. Specification No. 58,355.

The heat transfer device may serve various purposes. lt may beadvantageous for reasons of space to arrange the heat source at adistance from the heater; for example, in vehicles may be equipped witha thermodynamic engine, in which the heat is furnished by are-chargeable heat accumulator arranged elsewhere in the vehicle. Thenature of the heat source may involve the desirability or necessity todispose the machine at a distance from said source, for example, whenthe heat is supplied from a nuclear reactor, and when the machine has tobe protected from the dangers .of the radiation released by the nuclearreactions and the like. It may furthermore be advantageous to use thattransfer device for establishing a thermal contact between the heatersof a number of thermodynamic machines or the various heaters of amulti-cylinder thermodynamic engine and one and the same common heatsource.

In the above-mentioned cases, practice gives rise to a problem: theinterruption of the heat transfer from the heat source to the heater.If, for example, a plurality of heaters of one or more machinescommunicate through separate heat transfer devices with the same heatsource, and if the heat transport to one of said heaters has to beinterrupted, for examplem because the machine is stopped or because thepower of a multicylinder thermodynamic engine is reduced by putting acylinder out of operation, the heat supply from the heat source to thefurther machines or cylinders has to be continued. It is then notallowed to arrest the production of heat by the heat source, if this ispossible; nor neither is it allowed to remove the heat source. Thelatter encounters frequent practical difficulties, particularly when theheat source is a heat accumulator forming an integral part of the heattransfer device.

The heat transfer device usually forms part of the machine, so thatinterruption of the heat transport by removal of the heat transferdevice would require a time-consuming dismounting operation, the moredifficult on account of the high heater temperatures, which may exceed700 C in thermodynamic engines. Finally also turning away and/ordisplacing of the heat transfer device in conjunction or not inconjunction with the machine with respect to the heat source areattended by great practical inconveniences.

THE NEW INVENTION The present invention has for its object to provide ahot-gas machine comprising a heat transfer device, in which the heattransport from the heat source to the heater can be interrupted in asimple, rapid manner.

The hot-gas machine in accordance with the invention is characterized inthat the heat transfer device comprises at least two closed spacescontaining a heat transporting medium and arranged one after the otherin the direction of heat transport; the distal ends of these spaces areprovided with heat-passing walls through which heat from the heat sourcecan be conducted to the transporting medium, or the latter can give offheat to the heater, the proximal ends of said spaces having furtherheat-passing walls between which a switching element is provided forestablishing a thermal contact between said further walls.

In this way a machine is obtained in which the heat transfer from theheat source to the heater can be interrupted simply by actuating theswitching element.

If the place of condensation of a space is located at a higher levelthan the place of evaporation, the return of condensate from thecondensation place to the evaporation place may be performed under theaction of the force of gravity. If this is not the case, each space ofan advantageous embodiment of the machine in accordance with theinvention may comprise a porous mass of material which connects the heatpassing wall with the further heat-passing wall. By the capillary actionof this mass of material, the reflow of condensate may then also takeplace without contribution of the force of gravity and even against theforce of gravity. This means a great independence of position of themachine comprising a heat transfer device.

In a further advantageous machine embodying the invention the switchingelement is formed by a reservoir having two heat-passing reservoirwalls, which are each in contact with a further heat-passing wall or arealso formed by a further heat-passing wall, the reservoir containing aheat transporting medium of variable pressure and/or quantity.

The heat transporting medium in the reservoir may be formed by a liquidwhich always remains in the same state of aggregation. A decrease of thequantity of liquid in the reservoir results in a decrease of the flow ofheat between the two heat-passing walls of the reservoir. The heattransfer is blocked, when the whole quantity of liquid is removed fromthe reservoir.

A further advantageous machine embodying the invention is characterizedin that the heat transportingmedium in the reservoir conducts heat froma hot heatpassing wall to a cold one of the reservoir while the liquidchanges over to the vapor phase when heat is absorbed from the hotheat-passing wall and the vapor changes over to the liquid phase whenheat is given off to the cold heat-passing wall; there is provided anauxiliary reservoir having portions serving as a liquid space and as avapor space respectively and being in open communication with thereservoir through a vapor duct connected with the vapor space; theauxiliary reservoir is capable of absorbing cold from a cold source forcondensing and/or solidifying the transportingmedium in the liquid spaceand of absorbing heat from a heat source for melting and/or evaporatingthe transportingmedium in said liquid space. In operation of themachine, only vaporous transporting-medium can flow from the reservoirto the auxiliary reservoir or conversely. Transporting-medium condensedor solidified in the auxiliary reservoir is retained therein and istherefore no longer available for the heat transfer between the two heatpassing walls of the reservoir. By storing a greater or smaller quantityof transporting-medium in the liquid phase and/or solid phase in theauxiliary reservoir, a smaller or greater heat transfer will occur fromthe hot reservoir heat passing wall to the cold heat-passing wall of thereservoir.

Apart therefrom it is possible by increasing the pressure in thereservoir, for example, by admitting an inert, compressed gas into thereservoir, to raise the boiling point of the heat transporting-medium sothat the increased boiling point exceeds the operational temperature ofthe hot heat-passing wall of the reservoir. The transporting-medium isthen no longer evaporated and the heat transfer between the heat-passingwalls of the reservoir is arrested.

According to the invention the aforesaid auxiliary reservoir may be inopen communication with the reservoir also through a liquid ductconnected with the liquid space of the auxiliary reservoir for passingtransporting-medium from the auxiliary reservoir to the reservoir; thisliquid duct includes a liquid trap adapted to be cooled, in which liquidtransporting medium can be solidified for closing the liquid duct. Thisprovides the advantage that transporting medium to be conducted backfrom the auxiliary reservoir to the reservoir need not be firstevaporated, but can flow back in the liquid phase. By freezing theliquid trap the flow of liquid can be arrested so that the wholequantity of transporting medium condensed or solidified in the auxiliaryreservoir is kept therein.

In an advantageous machine embodying the invention the liquid trap isformed by at least a portion of the liquid duct comprising a porousfilling mass.

A further advantageous machine embodying the invention is characterizedin that the reservoir comprises a porous mass of material, whichinterconnects the heat passing walls of the reservoir. If the heattransport in the reservoir is carried out by an evaporation-condensationprocess between the two heat passing walls of the reservoir, thetransporting medium condensed on the colder wall can readily beconducted back to the hotter wall without the action of gravity oragainst gravity by the capillary action of the suitably chosen porousmass of material. According to the invention the reservoir mayaccommodate radiation screens for preventing heat transfer by radiationbetween the heat passing walls of the reservoir.

The invention furthermore relates to a heat transfer device of the kindset forth. Although the transfer device is particularly suitable for usein thermodynamic engines, its use is not restricted thereto. Theinvention will be described more fully with reference to the drawing,which shows a few embodiments schematically not to scale.

DESCRIPTION OF THE DRAWINGS FIG. 1 shows a hot-gas engine comprising aheat transfer device, in which the switching element is formed by aliquid layer in a reservoir between the two spaces.

FIGS. 2 and 3 show hot-gas engines, in which the reservoir serving as aswitching element comprises a medium which transports heat by means ofan evaporation-condensation process, the pressure of said medium beingvariable by the supply or outlet of an inert gas in the reservoir.

FIGS. 4 and 5 show a hot-gas engine in which the reservoir serving as aswitching element comprises a medium transporting heat by means of anevaporationcondensation process, which medium can be withdrawn holly orpartly from the reservoir and be stored in an auxiliary reservoircommunicating therewith.

FIGS. 6a and 6b each show two hot-gas engines communicating each via aheat transfer device with a common heat source, each transfer devicecomprises as a switching element a reservoir in which a medium iscontained which transports heat by means of an evaporation-condensationprocess and which medium can be stored wholly or partly in an auxiliaryreservoir.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, referencenumeral 1 designates the cylinder of a hot-gas engine in that part inwhich in operation the cyclic medium is constantly at a hightemperature. The cylinder comprises a displacer 2 which is capable ofdisplacing hot cyclic medium from the expansion space 4 towards the coldside of the engine by moving upwardly and by means of a driving gear(not shown) connected with the displacer rod 3. The cyclic medium passesthrough a heater 5, a regenerator 6 and a cooler 7. Heat can be suppliedfrom without through the wall of the which is a heat exchanger to thecyclic medium in the expansion space 4. The wall of the heater 5 forms aheat passing wall 8 of a closed space 9, which forms part of a heattransfer device 10. The space 9 has furthermore a further heat passingwall 11 and is otherwise thermally isolated from the surroundings.

The heat transfer device 10 comprises furthermore a closed space 12comprising on the one hand a heat passing wall 13 and on the other handa further heat passing wall 14, and being otherwise thermally isolatedfrom the surroundings. The further heat passing walls 11 and 14 form, inaddition, heat passing walls of a reservoir 15, which is otherwisethermally isolated from the surroundings. The term heat passing wall hasto denote a wall having low thermal resistivity. These are not onlywalls of material of high thermal conductivity but also walls ofmaterials of lower thermal conductivity, provided the thickness of thewall is sufficiently small.

The further heat passing wall 13 of the space 12 is in thermal contactwith a heat source 16 of high temperature, which may be a heataccumulator storing latent heat and/or sensible heat. The heataccumulator may be secured to the heat passing wall 13 or it may bearranged separately therefrom. As an alternative, the heat accumulatormay be arranged inside the space 12; it has then to be possible torecharge the heat accumulator after use. The spaces 9 and 12 are bothfilled partly with a suitably chosen quantity of liquid transportingmedium, which can evaporate at the temperature level of the heat source.

With a view to the high temperatures (about 700 C) of the heater of thehot-gas engine, suitable transporting media are, for example, the metalssodium, potassium, lithium, cadmium, cesium, metal salts such as themetalogenes, zinc chloride, aluminum bromide, cadmium iodide, calciumiodide, zinc bromide or mixtures thereof. Suitable for use arefurthermore nitrates, nitrites or mixtures thereof.

The reservoir 15 contains a liquid which forms a thermal connectionbetween the further heat passing walls 11 and 14. In the operation ofthe hot-gas engine the liquid layer remains in the liquid phase. It maybe chosen in accordance with the choice of the transporting medium inthe spaces 9 and 12 determined by the temperature of the heater of theheat source.

A liquid inlet 17 and a liquid outlet 18 communicate with the reservoir15. The thermal expansion of the small quantity of liquid in thereservoir 15 may be compensated for by connecting an expansion vesselwith the liquid inlet 17, which is not shown in the drawing.

The device operates as follows: The heat source 16 supplies heat throughthe heat passing wall 13 to theliquid transporting medium inside thespace 12 on said wall. This transporting medium evaporates and moves tothe further heat passing wall 14 owing to the locally prevailing lowvapor pressure as a result of the comparatively low local temperature.The movement of the vapor is indicated by broken arrow lines, The vaporthen condenses on the further heat passing wall 14, while giving offevaporation heat to said wall. Under the action of gravity thecondensate flows back to the heat passing wall 13, where it is againevaporatedThe flow of the condensate is indicated by full arrows. Theheat absorbed by the further heat passing wall 14 passes through theliquid layer in the reservoir 15 and through the further heat passingwall 11 to the space 9 and causes evaporation of liquid transportingmedium contained inside said space on the further heat passing wall 11.The evaporation-condensation process performed inside the space 9 isidentical to that in the space 12. The evaporation heat released by thecondensation of transporting medium on the heat passing wall 8 passesthrough said wall to the cyclic medium in the expansion space 4 in orderto compensate for the caloric energy converted into mechanical energyduring the expansion of the cyclic medium and also in order tocompensate for the normal caloric losses.

If the heat transport from the heat source 16 to the heater 5 has to beinterrupted, for example, for stopping the engine, this can be carriedout in a simple manner by removing the liquid from the reservoir 15 viathe liquid outlet 18 and, if necessary, by further exhausting thereservoir 15. Even if the heat source 16 continues supplying heat, forexample, if it is a heat accumulator, the supplied heat cannot attainthe heater 5. The sole consequence is that an evaporation-condensationprocess is performed only inside the space 12 until the vapor pressurein the portion of the space 12 adjacent the further heat passing wall 14is equal to the vapor pressure at the heat passing wall 13, the latterbeing determined by the temperature of the heat source 16. As a matterof course, the space 12 has to be structurally formed so that its wallscan withstand the potential maximum vapor pressure.

In the device shown in FIG. 1 a small quantity of heat will always leakfrom space 12 to space 9 due to thermal radiation from the further heatpassage wall 14 to the further heat passage wall 11. This may, ingeneral, be prevented by arranging radiation screens in the reservoir,which screens block the passage of thermal radiation.

In the device shown in FIG. 2 corresponding parts are designated by thesame reference numerals as in FIG. 1. The reservoir 15 accommodatesradiation screens 19, which prevent the radiation heat from the furtherheat passing wall 14 from reaching the further heat passing wall 11. Thereservoir 15 is partly filled with liquid transporting medium.

The operation of this device differs from that of FIG. 1 only to anextend such that in operation heat supplied by the further heat passingwall 14 to the reservoir 15 produces evaporation of liquid transportingmedium in said reservoir. The resultant vapor moves towards the regionof low vapor pressure, that is to say, near the comparatively coldfurther heat passing wall 1 1. It condenses on said wall while givingoff the released condensation heat and under the action of the gravitycomponent it flows along the slope of the reservoir as a liquid back tothe further heat passing wall 14, where the liquid evaporates again. Aduct 20 communicates with the reservoir and includes a cook 21, which isadapted to establish a communication between the reservoir 15 and eitherthe gas cylinder 22 containing a compressed inert gas or a pumpingdevice 23. Between the cock 21 and the gas cylinder 22 a pressurereducing valve 24 is provided and between the cock 21 and the pumpingdevice 23 a vapor trap 25 is arranged for transporting medium.

If the heat transport from the heat source 16 to the heater 5 has to beinterrupted, inert gas is supplied from the gas cylinder 22 to thereservoir 15. The pressure'of the inert gas produces such as increase inthe boiling point of the transporting medium in the reservoir 15 thatthe new boiling point exceeds the temperature of the further heatpassing wall 14. The evaporation of liquid transporting medium in thereservoir is then stopped and hence also the heat transport from thefurther heat passing wall 14 to the further heat passing wall 1 1.

When the heat transport has to be restored, the reservoir 15 iscommunicated with the pumping device 23, which pumps away the inert gasfrom the reservoir 15. Any medium vapor carried along with the inert gascan condensate in the vapor trap 25 by cooling and be held therein.

Obviously all kinds of shapes and dispositions as, for example, those ofFIG. 1, are possible provided it is ensured that condensate can flowback to the place of evaporation.

FIG. 3 shows a device which is substantially identical to that of FIG.2. Corresponding parts are designated by the same reference numerals asin FIG. 2. The device shown in FIG. 3 difiers essentially from that ofFIG. 2 by the presence of porous masses of material 26, 27 and 28 on theinner walls of the space 9, the reservoir 15 and the space 12. Theseporous masses of material have such a capillary structure that byutilizing the surface tension of the liquid transporting medium in thespace or the reservoir respectively, in the given operational state ofthe space or the reservoir respectively, they are capable of conductingby capillary action the condensate formed on the comparatively cold heatpassing wall, on the heat passing wall of the space or on the reservoirrespectively back to the comparatively hot heat passing wall, thefurther heat passing wall of the space or the reservoir respectively.

In this way a flow-back of condensate is possible without using theforce of gravity or in the absence of the gravitational acceleration,and even against this acceleration. This provides great freedom in thedisposition of the hot-gas engine and in the disposition or constructionof the various parts of the heat transfer device.

In the assembly of FIG. 3, in which the heat transfer device is arrangedin a horizontal plane, flow-back of condensate is performed in spite ofthe horizontal position. This is performed in space 12 by the absorptionof condensate formed at the further heat passing wall 14 in the porousmass of material 28, which conveys the condensate by capillary effect tothe heat passing wall 13.

In a similar manner condensate in reservoir 15 is conveyed from thefurther heat passing wall 11 to the further heat passing wall 14 via theporous mass of material 27 and in space 9 from the heat passing wall 8to the further heat passing wall 11 via the porous mass of material 26.

The operation of the device shown in FIG. 3 is otherwise similar to thatof FIG. 2 so that further description is dispensed with.

The porous mass of material may be formed by ceramic material, by wireortape-shaped material of metal or metal alloys or by an array of tubesand the like. The choice depends inter alia upon the chosen heattransporting medium and on the prevailing temperatures in the operationof the device.

FIG. 4 shows a hot-gas engine comprising a heat transfer device betweenthe heater and the heat source, the difference from that of FIG. 3 beingthat the reservoir 15 in the present case is in open communicationthrough a vapor duct 29 with an auxiliary reservoir 30, in which aheating coil 31 and a cooling coil 31 are arranged. If the heat transferbetween the heat source 16 and the heater has to be interrupted, this isperformed by cooling the auxiliary reservoir 30. Owing to the lowtemperature then prevailing in the auxiliary reservoir transportingmedium vapor will flow through the vapor duct 29 from the reservoir tothe auxiliary reservoir, in which it will condense or even solidify. Itis thus possible to withdraw the whole quantity of medium from thereservoir 15 and to store it in the auxiliary reservoir 30. In theabsence of medium in the reservoir 15 the heat transfer is blocked. Ifthe heat transfer has to be restored, heat is conducted to the auxiliaryreservoir 30, in this case by means of the heating coil 31, so thatmedium evaporates from the auxiliary reservoir 30 and flows back to thereservoir 15 via the vapor duct 29. In order to maintain the restoredheat transfer, heat, be it a small value, has constantly to be suppliedto the auxiliary reservoir 30 in order to avoid that the temperature andhence the vapor pressure inside the auxiliary reservoir 30 drop belowthose at the further heat passing wall 11. This might give rise to aflow of medium vapor from the further heat passing wall 14 to theauxiliary reservoir 30, in which it would condense instead of travellingon to the further heat passing wall 1 l, where it has to condense.

In the device shown in FIG. 4 medium condensed or solidified in theauxiliary reservoir 30 has first to be evaporated before the return tothe reservoir 15 is possible and in operation the auxiliary reservoir 30has to be kept hot.

This is contrary to the device shown in FIG. 5, which coarselycorresponds with that of FIG. 4, there being provided, however, a liquidduct 32 joining on the one hand that portion of the auxiliary reservoir30 in which liquid or solidified medium can be stored and on the otherhand the reservoir 15. The liquid duct 32 includes a porous filling mass33, which contributes to the use of the liquid duct 32 in addition as aliquid trap. The liquid duct 32 can be cooled for this purpose and canbe heated with the aid of the heating coil 31, which surrounds hereinnot only the auxiliary reservoir 30 but also the liquid duct 32.

In order to interrupt the heat transport between the heat source 16 andthe heater 5 the auxiliary reservoir 30 and the liquid duct 32 arecooled. Then medium vapor is again conveyed from the reservoir 15through the vapor duct 29 to the auxiliary reservoir 30. This vapor iscondensed and solidified in the auxiliary reservoir. This operationcontinues until the reservoir 15 has become dry, so that the heattransfer in this reservoir is cut off.

By the capillary action of the porous filling mass 33 the liquid duct 32is completely filled with liquid. It is thus avoided that medium vaporfrom the reservoir 15 penetrates into the liquid duct 32, which wouldrender solidification impossible due to the high heat content of thisvapor.

The porous filling mass 33 performs during the solidification processalso the function of flow resistor, which ensures that liquid medium canpass only with comparatively low speed through the liquid duct 32 sothat owing to this low speed solidification of liquid in the liquid duct32 is additionally facilitated. The passage is then cut off so that theliquid medium can readily solidify in the auxiliary reservoir 30.

Even without porous filling mass it is possible to cause solidificationof liquid in the liquid duct 32, for example, by constructing a portionof the liquid duct in the form of a bend, which is filled with liquidand cooled.

If the heat transfer has to be restored, the solid medium in theauxiliary reservoir 30 and the liquid duct 32 is melted with the aid ofthe heating coil 31. By the capillary action of the porous filling mass33 and in this case also under the action of gravity liquid medium flowsfrom the auxiliary reservoir 30 via the liquid duct 32 into the porousmass 27 of reservoir 15 and moves towards the further heat passing wall14, where it is evaporated. The evaporation-condensation process insidethe reservoir 15 and hence the heat transfer are thus restored.

The further operation of this device is identical to that of the deviceshown in FIG. 4.

FIGS. 6a and 6b show assemblies in which two hotgas engines communicateeach via a heat transfer device with a single common heat source.

Since the construction and the operation of the heat transfer devices ofFIG. 6a are identical to those of the device of FIG. 5, a furtherdescription may be dispensed with. Corresponding parts are designated bythe same reference numerals as in FIG. 5. The device shown permits in asimple manner of interrupting or restoring at will the heat transferfrom the heat source 16 to the heater of a hot-gas engine or to theheater of the two hot-gas engines. This is particularly important whenthe heat source is formed by a heat accumulator, which supplies heatcontinuously to the spaces 12. By interrupting the heat transfer in aheat transfer device from the space 12 to the space 9 by means of thereservoir 15, a thermal equilibrium is established between the heataccumulator 16 and the space 12 concerned.

The device shown in FIG. 6b differs from that shown in FIG. 6a only tosuch an extent that the two heat transfer devices have a common space 12having a single heat passing wall 13, through which heat from the heatsource 16 can be supplied to the medium inside the space 12. At the heatpassing wall 13 in the space 12 medium evaporates and flows in twodirections towards the two further heat passing walls 14 of the space12, where it condenses, while giving off its condensation heat. Thecondensate is conducted by the capillary action of the appropriatelychosen porous mass of material 28 back to the heat passing wall 13,where it evaporates again.

Interruption or restoration of the heat transfer from the heat source 16to one or both heaters 8 are performed in the same manner as describedwith reference to FIG. 5.

In the devices of the kind shown in FIGS. 4, and 6 the switching elementmay also be a reservoir filled with a liquid forming a thermallyconducting layer between the further heat passing walls 11 and 14. Aregulation of the liquid level then results in a control of the heatpassing surface and hence of the heat transfer.

In the arrangement shown in the drawing the further heat passing wallsof the spaces 9 and 12 also form the heat passing walls of the reservoir15. Obviously, the reservoir may have its own heat passing walls, whichare in contact with the further heat passing walls of the spaces 9 and12.

What is claimed is:

1. A hot-gas machine such as a hot-gas reciprocating engine or turbine,in which a gaseous medium performs a closed thermodynamic cycle, saidmachine comprising a heat exchanger in which the cyclic medium receivesheat from without from a heat source, such as a heat accumulator, and aheat transfer device being arranged between the heat source and the heatexchanger, and containing a heat-transporting medium which absorbs heatfrom the heat source while changing from the liquid to the vapor phase,and gives off heat to the heat exchanger while changing from the vaporto the liquid phase, characterized in that the heat transfer devicecomprises at least two closed spaces containing heat-transporting mediumand arranged one after the other in the direction of heat transport, thedistal ends of said spaces being provided with heatpassing walls throughwhich heat from the heat source can be supplied to the transportingmedium and through which the medium can give off heat to the heatexchanger, whereas the proximal ends of said spaces comprise furtherheat-passing walls between which a switching element is provided forestablishing a thermal contact between said further walls.

2. A machine as claimed in claim 1 characterized in that each spacecomprises a porous mass of material which connects the heat-passing wallwith the further heat-passing wall.

3. A machine as claimed in claim 1 characterized in that the switchingelement is formed by a reservoir having two heat-passing walls, each ofwhich is in contact with a further heat-passing wall or which are formedalso by a further heat-passing wall, the reservoir containing a heattransporting medium, the pressure and the quantity of which can becontrolled.

4. A machine as claimed in claim 3 characterized in that the heattransporting medium in the reservoir transports heat from a hotheat-passing wall to a cold heat-passing wall of the reservoir whilechanging from the liquid phase to the vapor phase at the absorption ofheat from the hot heat-passing wall of the reservoir and while changingfrom the vapor phase to the liquid phase when giving off heat to thecold heat-passing wall of the reservoir, there being provided anauxiliary reservoir comprising a portion operating as a liquid space anda portion operating as a vapor space, the auxiliary reservoir being inopen communication with the reservoir through a vapor duct connectedwith the vapor space, the auxiliary reservoir being capable of absorbingcold from a cold source for condensing and/or solidifying transportingmedium in the liquid space or of absorbing heat from a heat source formelting and/or evaporating transporting medium in said liquid space.

5. A machine as claimed in claim 4 characterized in that the auxiliaryreservoir also is in open communication with the reservoir via a liquidduct connected with the liquid space of the auxiliary reservoir, throughwhich duct liquid transporting medium can flow from the auxiliaryreservoir to the reservoir, said liquid duct comprising a liquid trapwhich can be cooled and in which liquid transporting medium can solidifyfor cutting off the liquid duct.

6. A machine as claimed in claim 5 characterized in that the liquid trapis formed by at least a portion of the liquid duct in which a porousfilling mass is arranged,

7. A machine as claimed in claim 3, characterized in that the reservoircomprises a porous mass of material, which interconnects the heatpassing walls of the reservoir.

8. A machine as claimed in claim 3 characterized in that the reservoiraccommodates radiation screens for preventing heat transfer by radiationbetween the heat passing walls of the reservoir.

9. A hot-gas engine in which a gaseous medium performs a closedthermodynamic cycle, said machine operable with a heat source andincluding a heatexchanger in which said gaseous medium receives heatfrom said source, and a heat transfer device which contains aheat-transporting medium and is disposed between the heat source and theheat exchanger, this transfer device comprising means defining at leasttwo closed spaces containing said heat-transporting medium, these spacespositioned sequentially and thus having two remote, distal ends and twoadjacent proximal ends, each of said ends comprising a heat-passingwall,

whereby heat is cyclically transmitted through one distal endewall fromthe heat source to said heat-transporting medium in one space, whichmedium then changes from liquid to vapor phase, and through the otherdistal end wall of said other space from said heattransporting mediumtherein to the heat-exchanger, which medium then changes from vapor toliquid phase, said device further comprising a switching element betweensaid proximal end-walls for establishing a thermal contact therebetween.

10. Apparatus according to claim 9 comprising a porous mass within saidspaces which mass connects each remote wall with a proximal wall of eachspace.

11. Apparatus according to claim 9 wherein said switching elementcomprises a main reservoir having two heat-passing walls, each of whichis in contact with a proximal heat-passing wall, the reservoircontaining a heat-transporting medium, the pressure and the quantity ofwhich can be controlled.

12. Apparatus according to claim 11 wherein said heat-transportingmedium in the main reservoir transports heat from a hot heat-passingwall to a cold heatpassing wall of the main reservoir while changingfrom the liquid phase to the vapor phase at the absorption of heat fromthe hot heat-passing wall of the main reservoir and while changing fromthe vapor phase to the liquid phase when giving off heat to the coldheatpassing wall of the main reservoir, the apparatus further comprisingan auxiliary reservoir having a portion operating as a liquid space anda portion operating as a vapor space, the auxiliary reservoir being inopen communication with the main reservoir through a vapor ductconnected with the vapor space, the auxiliary reservoir being capable ofabsorbing cold from a cold source for condensing and/or solidifyingtransporting medium in the liquid space or of absorbing heat from a heatsource for melting and/or evaporating transporting medium in said liquidspace.

13. Apparatus according to claim 12 wherein said auxiliary reservoiralso is in open communication with the main reservoir via a liquid ductconnected with the liquid space of the auxiliary reservoir, throughwhich duct liquid transporting medium can flow from the auxiliaryreservoir to the reservoir, said liquid duct comprising a liquid trapwhich can be cooled and in which liquid transporting medium can solidifyfor cutting off the liquid duct.

14. Apparatus according to claim 13 wherein said liquid trap is formedby at least a portion of the liquid duct in which a porous filling massis arranged.

1. A hot-gas machine such as a hot-gas reciprocating engine or turbine,in which a gaseous medium performs a closed thermodynamic cycle, saidmachine comprising a heat exchanger in which the cyclic medium receivesheat from without from a heat source, such as a heat accumulator, and aheat transfer device being arranged between the heat source and the heatexchanger, and containing a heat-transporting medium which absorbs heatfrom the heat source while changing from the liquid to the vapor phase,and gives off heat to the heat exchanger while changing from the vaporto the liquid phase, characterized in that the heat transfer devicecomprises at least two closed spaces containing heat-transporting mediumand arranged one after the other in the direction of heat transport, thedistal ends of said spaces being provided with heat-passing wallsthrough which heat from the heat source can be supplied to thetransporting medium and through which the medium can give off heat tothe heat exchanger, whereas the proximal ends of said spaces comprisefurther heat-passing walls between which a switching element is providedfor establishing a thermal contact between said further walls.
 2. Amachine as claimed in claim 1 characterized in that each space comprisesa porous mass of material which connects the heat-passing wall with thefurther heat-passing wall.
 3. A machine as claimed in claim 1characterized in that the switching element is formed by a reservoirhaving two heat-passing walls, each of which is in contact with afurther heat-passing wall or which are formed also by a furtherheat-passing wall, the reservoir containing a heat transporting medium,the pressure and the quantity of which can be controlLed.
 4. A machineas claimed in claim 3 characterized in that the heat transporting mediumin the reservoir transports heat from a hot heat-passing wall to a coldheat-passing wall of the reservoir while changing from the liquid phaseto the vapor phase at the absorption of heat from the hot heat-passingwall of the reservoir and while changing from the vapor phase to theliquid phase when giving off heat to the cold heat-passing wall of thereservoir, there being provided an auxiliary reservoir comprising aportion operating as a liquid space and a portion operating as a vaporspace, the auxiliary reservoir being in open communication with thereservoir through a vapor duct connected with the vapor space, theauxiliary reservoir being capable of absorbing cold from a cold sourcefor condensing and/or solidifying transporting medium in the liquidspace or of absorbing heat from a heat source for melting and/orevaporating transporting medium in said liquid space.
 5. A machine asclaimed in claim 4 characterized in that the auxiliary reservoir also isin open communication with the reservoir via a liquid duct connectedwith the liquid space of the auxiliary reservoir, through which ductliquid transporting medium can flow from the auxiliary reservoir to thereservoir, said liquid duct comprising a liquid trap which can be cooledand in which liquid transporting medium can solidify for cutting off theliquid duct.
 6. A machine as claimed in claim 5 characterized in thatthe liquid trap is formed by at least a portion of the liquid duct inwhich a porous filling mass is arranged,
 7. A machine as claimed inclaim 3, characterized in that the reservoir comprises a porous mass ofmaterial, which interconnects the heat passing walls of the reservoir.8. A machine as claimed in claim 3 characterized in that the reservoiraccommodates radiation screens for preventing heat transfer by radiationbetween the heat passing walls of the reservoir.
 9. A hot-gas engine inwhich a gaseous medium performs a closed thermodynamic cycle, saidmachine operable with a heat source and including a heat-exchanger inwhich said gaseous medium receives heat from said source, and a heattransfer device which contains a heat-transporting medium and isdisposed between the heat source and the heat exchanger, this transferdevice comprising means defining at least two closed spaces containingsaid heat-transporting medium, these spaces positioned sequentially andthus having two remote, distal ends and two adjacent proximal ends, eachof said ends comprising a heat-passing wall, whereby heat is cyclicallytransmitted through one distal end-wall from the heat source to saidheat-transporting medium in one space, which medium then changes fromliquid to vapor phase, and through the other distal end wall of saidother space from said heat-transporting medium therein to theheat-exchanger, which medium then changes from vapor to liquid phase,said device further comprising a switching element between said proximalend-walls for establishing a thermal contact therebetween.
 10. Apparatusaccording to claim 9 comprising a porous mass within said spaces whichmass connects each remote wall with a proximal wall of each space. 11.Apparatus according to claim 9 wherein said switching element comprisesa main reservoir having two heat-passing walls, each of which is incontact with a proximal heat-passing wall, the reservoir containing aheat-transporting medium, the pressure and the quantity of which can becontrolled.
 12. Apparatus according to claim 11 wherein saidheat-transporting medium in the main reservoir transports heat from ahot heat-passing wall to a cold heat-passing wall of the main reservoirwhile changing from the liquid phase to the vapor phase at theabsorption of heat from the hot heat-passing wall of the main reservoirand while changing from the vapor phase to the liquid phase when givingoff heat to the cold heat-passing wall of the main reservoir, theapparatus further comprising an auxilIary reservoir having a portionoperating as a liquid space and a portion operating as a vapor space,the auxiliary reservoir being in open communication with the mainreservoir through a vapor duct connected with the vapor space, theauxiliary reservoir being capable of absorbing cold from a cold sourcefor condensing and/or solidifying transporting medium in the liquidspace or of absorbing heat from a heat source for melting and/orevaporating transporting medium in said liquid space.
 13. Apparatusaccording to claim 12 wherein said auxiliary reservoir also is in opencommunication with the main reservoir via a liquid duct connected withthe liquid space of the auxiliary reservoir, through which duct liquidtransporting medium can flow from the auxiliary reservoir to thereservoir, said liquid duct comprising a liquid trap which can be cooledand in which liquid transporting medium can solidify for cutting off theliquid duct.
 14. Apparatus according to claim 13 wherein said liquidtrap is formed by at least a portion of the liquid duct in which aporous filling mass is arranged.